1. Field of the Invention
The present invention relates to a sealing structure between a plurality of parts which are joined together, and more particularly to a sealing structure using a liquid gasket.
2. Description of the Related Art
There are cases where a liquid gasket composed of uncured synthetic rubber is used to secure air-tightness and liquid-tightness between two parts which are joined together, such as a cylinder block and an oil pan or a cylinder head. In a case where this liquid gasket is used in a portion to which large pressure is applied or a portion which undergoes large thermal deformation, if its thickness is excessively small, the liquid gasket is incapable of following the displacement between the two parts, making it impossible to obtain satisfactory sealing properties in some cases.
As a countermeasure against such a problem, a structure is known in which a recessed portion for inserting and fitting the liquid gasket is formed on the joining surfaces of the two parts (refer to Japanese Utility Model Examined Publication Hei.5-34385).
However, a further reduction in the manufacturing cost is generally desired for mass-produced items, so that the structure which requires machining for forming the recessed portion is not preferable since the reduction in the number of manufacturing steps is difficult, as described in the aforementioned publication;
The invention has been devised to overcome the above-described problems of the related art, and its main object is to provide a sealing structure which is improved to make it possible to secure sealing properties of a liquid gasket without increasing the number of manufacturing steps.
To attain the above object, according to the present invention, a plate-shaped gasket 23 is inserted between a plurality of parts with an edge (an inner peripheral edge of a chain accommodating hole 27 in the embodiment) of the plate-shaped gasket uneven such that portions of mutual joining surfaces of the plurality of parts to be joined to each other (a cylinder block 1 and a cylinder head, as well as a chain cover 22 and a sprocket casing portion 20 in the embodiment) directly oppose each other, and a liquid gasket 29 is filled in a gap G formed by the directly opposing portions of the plurality of parts and the uneven edge of the plate-shaped gasket.
According to this arrangement, since the thickness of the liquid gasket can be determined by the thickness of the plate-shaped gasket, and the region of application of the liquid gasket can be determined by the edge of the plate-shaped gasket, the amount of application of the liquid gasket can be minimized, and the operating efficiency improves. Further, the liquid gasket is made difficult to be subject to effects (heat, water, etc.) from the outside, and this arrangement is advantageous in improvement of the durability of the liquid gasket. In addition, since it becomes unnecessary to form a recessed portion for storing the liquid gasket by machining, the number of manufacturing steps is prevented from increasing.
Further, the invention described above is applied to the mutual joining surfaces of the plurality of parts which are joined together to form a first space portion (a space S1 in a chain accommodating hole in the embodiment) and a second space portion (a space S2 in a cylinder, that is, a space S2 as a combustion chamber in the embodiment) held under pressure higher than that of the first space portion. Specifically, a plate-shaped gasket is inserted between the plurality of parts with an edge of the plate-shaped gasket uneven on a first space portion side such that outer peripheral portions in the first space portion directly oppose each other; outer peripheral portions of mutual joining surfaces of the plurality of parts in the second space portion are opposed to each other in a state in which a bead portion 23a formed on the plate-shaped gasket is interposed therebetween; and a liquid gasket is filled in a gap formed by the directly opposing outer peripheral portions of the plurality of parts in the first space portion and the offset edge of the plate-shaped gasket.
According to this arrangement, since it is unnecessary to form a bead portion in the first space portion on the low pressure side, the structure of the gasket does not become complex. Moreover, it is possible to stabilize the sealing properties of the second space portion on the high pressure side, and it suffices if openings corresponding to the first space portion and the second space portion are formed in a common plate-shaped gasket, so that the number of parts of the plate-shaped gasket is prevented from increasing.